24 volt computer fan

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petertearai
petertearai Solar Expert Posts: 471 ✭✭✭✭
in General Solar Power Topics #1
Hi . My system was 12 volts with a 12 volt rv water pump. Strapped to the top of the pump i had a 7 watt 12 volt fan . This worked for 10 years or so, i think keeping the motor cool helped .
I have done a change to 24 volts now . considered a voltage step down unit for the 12 volt pump, however considering its age, got a new 24 volt pump. To this i added  a 24 volt fan. . have had 2 of these fans fail, i think maybe because of the increased voltage above the 24 volts . ie 29 volts for absorb.
So ....... think a resister in series with the fan may help , or a voltage regulter . What size resister ?  or would i be better with a small regulator  circuit ?
Any help would be appreciated 
Regards  Peter
2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,696 admin
    #2
    tWhat is the wattage/amperage of the fan?

    For example if 1/4 amp fan and you want 30-24=6 volt drop:

    V=IR, R=V/I = 6 volts / 0.25 amps = 24 ohms
    P=V*I= 6 volts * 0.25 Amps = 1.5 Watt minimum resistor size/power rating

    i don't think it will hurt the fan to use an in-line resistor... May start a little slow and may run a little slower RPM.

    Does the water pump run long enough to get hot? Most DC RV pumps use brushed motors--And frequently the brushes wear out--And you can replace them sometimes (depending on motor design).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #3
    Try to get a 36 volt fan. Then it will just run it at slightly reduced speed.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #4
    Get one of those 2 buck ebay dc to dc converters. That way you can adjust it to your perfect speed. eg:

    http://www.ebay.com/itm/LM2596HVS-LM2596HV-DC-DC-Adjustable-Step-Down-Buck-Converter-Power-Supply-Module-/310788581728

    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #5
    hi thanks for your reply's. . The watts on the 24 volt fans are i think still around 7 watts . The 24 volt fans are free, ie no cost , but still need them to run reliably. The instructions on the new pump say for intermittent use only . Still with cooling my old 12 volt pump would often run continuously for 2 hours or so , and was still serviceable when retired . Didnt look at the 12 volt pump instructions, but am informed most of rv pumps are not continuously rated . . Will look into both sugestions . thanks .
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #6
    Hi Zone blue  . I havnt used ebay , free shipping and only 2 bucks . Sounds 2 good to be true .Have you used this .?
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • Photowhit
    Photowhit Solar Expert Posts: 6,017 ✭✭✭✭✭
    #7
    eBay Stuff that comes from China, can take a long time and sometimes doesn't make it at all. I had 2 sets of 5 - 6inch stainless rules, that I was refunded after they passed the expected delivery dates of 6 weeks and 10 weeks. I usually have received the items purchased from china, and for the most part have been what they said they were, Cheap water pump, 'T' amps, bearings, star bit screw drivers...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    if you are burning out 24v fans, you may be slowly killing your pump motor too.....
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #9
    good point .was hoping the pump would be designed for absorb voltage .
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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